Response of cassava to water deficit: Leaf area growth and abscisic acid

Cassava (Manihot esculenta Crantz) responds to decreases in water status by pronounced stomatal closure and decreased leaf area growth. Many water deficit responses are thought to be regulated by abscisic acid (ABA). To evaluate the extent to which ABA accumulated in a temporal pattern related to water deficit and leaf area growth, five cassava genotypes were grown in greenhouse conditions and subjected to water deficit and recovery treatments during the vegetative-growth stage. Young and mature leaves were sampled for analysis of area growth and ABA. Under water deficit, leaves from all genotypes rapidly accumulated large amounts of ASA in both mature and young leaves. Correspondingly, young leaves halted leaf expansion growth and transpiration rate decreased. Young leaves accumulated more ABA than mature leaves in both the control and stressed treatments. The high ABA levels under water deficit were completely reversed to control levels after 1 d of rewatering, This rapid return to control ABA levels corresponded with a rapid recovery of leaf area growth rates. We postulate that the rapid reduction in leaf area growth and stomatal closure observed in our study may be due to cassava's ability to rapidly synthesize and accumulate ABA at an early phase of a water deficit episode.